Create and edit playlist modals now upload/preview a cover image
(reusing the presigned-upload flow already used for tracks) and share
identical layout and coloring. Adds a cover proxy route and wires
PlaylistArt to render a playlist's real cover before falling back to
the track mosaic/gradient.
Also reworks the playlist detail page: full-width borderless "Añadir
de tu biblioteca" table with listens count and click-to-play, drops
the empty-playlist placeholder message, and restyles the playlists
grid to match the rest of the app.
Expand the player store, split player controls (transport, seek, volume, track info), add Cover/PlaylistArt/NowPlaying UI primitives and a cover image proxy route.
Admin